Biochemical and vascular alterations caused by X-radiation which lead to interphase death in non-dividing or slowly dividing cells will be studied. Attention will be directed toward the radiosensitive rat thymocyte and the radioresistant hepatocyte. Comparisons will be made of radiation-induced metabolic alterations and repair processes in these cells to arrive at an explanation of their differences in radiosensitivity. Early metabolic derangements which can be related to cell death in terms of time, dose, and capacity for repair, and those which are involved in late tissue damage, will be of primary interest.